1. Field of the Invention
This invention relates to a robot arm type transport apparatus configured from a plurality of links connected for pivotal motion to each other, and more particularly to a robot arm type transport apparatus which has a function of detecting a held state of a transport object article. The present invention relates also to an arm type transport apparatus having a link mounted for pivotal motion, and more particularly to an arm type transport apparatus having a function of detecting the center position of a regular circular transport object article such as a wafer and correcting the positional displacement of the transport object article.
2. Description of the Related Art
Transport apparatus are known which transport a thin transport object article of a disk shape or regular circular shape such as a semiconductor wafer in accordance with a fabrication process. One of such transport apparatus is a robot arm type or arm type transport apparatus which is configured from a plurality of links connected in series for pivotal motion relative to each other through revolute joint sections, which are individually driven to rotate to take out transport object articles one by one from an accommodating case, in which the transport object articles are accommodated at a predetermined pitch, and transport the taken out transport object article.
In a robot arm of the robot arm type transport apparatus, a holding element for holding a transport object article is provided at an end effecter which is a first link at a distal end of the robot arm. As means for holding a transport object article, various means are available including means for holding by vacuum attraction, means for sandwiching using a mechanical chuck and means for merely receiving a transport object article. However, whichever means is used, it is necessary to detect whether or not the end effecter appropriately holds a transport object article.
As one of means for such detection, it is disclosed in Japanese Patent Laid-Open No. 2002-270674 to provide a sensor for detecting presence or absence of a transport object article such as a photo-sensor or an electrostatic sensor on the end effecter.
Meanwhile, in a general transport system, when a regular circular transport object article is transported to a processing apparatus, in order to correct displacement of the position of the regular circular transport object article and appropriately transport the regular circular transport object article, alignment is carried out using an apparatus called aligner. The direction upon alignment includes three-directions including X and Y directions and a θ direction which is the direction of an axis of rotation of the aligner.
Japanese Patent Laid-Open No. Hei 8-222611 discloses, as a method for aligning a regular circular transport object article, a method of detecting displacement of the regular circular transport object article in X, Y and θ directions to carry out alignment.